A single-cylinder engine is configured such that an exhaust pipe is directly connected to a cylinder head so as to discharge exhaust gas to the outside, while a multi-cylinder engine including two or more cylinders is configured such that an exhaust manifold is used to collect exhaust gas discharged from each cylinder and then to discharge the collected exhaust gas to the air through an exhaust pipe.
However, since the exhaust manifold is in contact with an exhaust port of a cylinder head and thus directly receives heat of high-temperature exhaust gas discharged from a combustion chamber, the exhaust manifold may be overheated and may repeatedly contract and expand, so that the exhaust manifold may not be able to tolerate the stress and may crack.
In addition, such a repeated contraction and expansion action may cause a phenomenon in which a bolt connecting manifolds loses the axial force thereof and is thus loosened.
For these reasons, in order to reduce the stress according to thermal expansion as described above, an exhaust manifold 10 is configured in such a manner that, as shown in FIG. 1, a front manifold 11 for a cylinder head side, a rear manifold 13 for a turbocharger side, and a center manifold 12 for connecting the front and rear manifolds are separately molded, and then are assembled by connecting corresponding contact ends to each other in a sliding contact way.
In addition, as shown in FIG. 2, in order to prevent leakage of exhaust gas through the junction parts of the manifolds, a sealing ring 14 is inserted into the connection part, and an expander 15 for assisting and maintaining a tension is disposed on the inner circumferential surface of the sealing ring 14.
Accordingly, the sealing operation of a sealing part is maintained by the sum of the tensions of the sealing ring 14 and the expander 15, and by a lateral pressure caused by the pressure of exhaust gas.
However, the lateral pressure caused by the pressure of exhaust gas is not sufficient in the case of a natural aspirated engine, and cannot arrive at a pressure enough to keep sealing in a low-speed section in the case of a turbocharged engine. The reason why gas is leaked although the pressure of the sealing ring 14 to the outer circumferential surface of the ring, caused by the sealing ring 14 and the expander 15, is maintained at an appropriate level is that the lateral pressure is not appropriately generated.
Accordingly, as shown in FIG. 3, a phenomenon in which exhaust gas is leaked through a chink of the connection part occurs, thereby polluting the circumference thereof and causing a turbo lag phenomenon, which is a chronic problem of a turbocharger.
Therefore, embodiments of the present invention are intended to provide an apparatus for enabling exhaust gas to smoothly flow without leaking to the outside due to a momentary negative-pressure increase by mounting a gas leakage prevention cover on the connection part of the exhaust manifold so that the speed of exhaust gas can increase while the exhaust gas is passing through the gas leakage prevention cover.
The information disclosed in this Background section is only for enhancement of understanding of the general background and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.